What is the recommended dose and duration of ampicillin (Ampicillin) for treating Enterococcus faecalis infections?

Ampicillin Dosing and Duration for Enterococcus faecalis Infections

For Enterococcus faecalis infections, the recommended dose of ampicillin is 2 grams IV every 4 hours for 4-6 weeks, with duration depending on the site of infection and clinical response. 1

Dosing Recommendations by Infection Type

Urinary Tract Infections

• Uncomplicated UTI: 500 mg orally four times daily 2
• Complicated UTI: 500 mg orally four times daily; severe infections may require larger doses 2
• High-dose for ampicillin-resistant VRE in UTI: 18-30 g IV daily in divided doses 1

Endocarditis

• Native valve endocarditis: 2 g IV every 4 hours for 4-6 weeks 1
  • 4 weeks if symptoms present <3 months
  • 6 weeks if symptoms present >3 months
• Prosthetic valve endocarditis: 2 g IV every 4 hours for at least 6 weeks 1

Combination Therapy Options

• For aminoglycoside-resistant strains: Ampicillin plus ceftriaxone 1, 3
  • Ampicillin 2 g IV every 4 hours
  • Ceftriaxone 2 g IV every 12 hours
  • Duration: 6 weeks regardless of symptom duration

Treatment Algorithm Based on Infection Site and Resistance Pattern

1. Identify infection site and severity:

   • UTI (uncomplicated vs complicated)
   • Endocarditis (native vs prosthetic valve)
   • Bacteremia
   • Other systemic infections

2. Check susceptibility testing:

   • Ampicillin-susceptible: Use ampicillin monotherapy
   • Aminoglycoside-resistant: Use ampicillin-ceftriaxone combination
   • Vancomycin-resistant: Consider high-dose ampicillin for UTI

3. Determine appropriate dosing:

   • Standard dose: 500 mg orally four times daily for UTI 2
   • High dose: 2 g IV every 4 hours for endocarditis and severe infections 1
   • Very high dose: 18-30 g IV daily in divided doses for resistant strains in UTI 1

4. Determine appropriate duration:

   • UTI: 48-72 hours after patient becomes asymptomatic 2
   • Endocarditis: 4-6 weeks depending on valve type and symptom duration 1
   • Other infections: Minimum 48-72 hours after patient becomes asymptomatic 2

Special Considerations

Pediatric Dosing

• Children weighing ≤20 kg: 100 mg/kg/day in 4 equally divided doses for GU/GI infections 2
• Children weighing >20 kg: Adult dosing 2

Administration Timing

• Administer at least 30 minutes before or 2 hours after meals for maximal absorption 2

Monitoring

• For endocarditis, monitor for clinical improvement and clearance of bacteremia
• For UTI, clinical appraisal is necessary during therapy and may be needed for several months afterward 2

Potential Pitfalls and Caveats

• Resistance concerns: E. faecalis can develop resistance to ampicillin. Recent studies show ampicillin remains effective against many E. faecalis isolates, but susceptibility testing is crucial 4
• Combination therapy: For serious infections like endocarditis, combination therapy may be necessary, especially with aminoglycoside-resistant strains 1, 3
• Duration of therapy: Insufficient treatment duration is a common pitfall. Ensure adequate duration based on infection site and clinical response 1
• Distinguishing colonization from infection: Particularly important in catheterized patients to avoid unnecessary treatment 5

The ampicillin-ceftriaxone combination has shown excellent efficacy for treating HLAR E. faecalis endocarditis with 100% cure rates in patients completing the protocol 3, making it a valuable option when aminoglycoside combinations cannot be used due to resistance or risk of nephrotoxicity.